1. Field of the Invention
The present invention relates to a check valve of the so-called xe2x80x9cduckbillxe2x80x9d type for use in drainage systems and effluent outfall lines.
2. Description of the Prior Art
A check valve is essentially a valve which allows fluid to flow in only one direction through a conduit, while closing and preventing back or reverse flow, when back pressure builds up downstream of the valve to a level greater than the upstream fluid pressure head. Check valves are used in various fluid transportation operations and must include some means of allowing the forward flow of liquid yet preventing any backflow.
Conventional rubber duckbill check valves have an inlet cuff, an outlet bill and a transitional middle part for connecting the cuff and the bill. The bill comprises a slit which opens when fluid is forced through the valve. Typically, existing xe2x80x9cduckbillxe2x80x9d type check valves have a bill slit dimension that is equal to or less than one-half the cuff (inlet) circumference. The reason for this is that if the bill slit dimension is larger than one-half the circumference of the cuff diameter, it becomes difficult or even impossible to remove a one-piece mandrel, which is used to manufacture the check valve through the cuff.
In most applications, it is desirable to have the maximum flow through the valve at the lowest possible pressure drop in the forward direction of the flow or, in other words, the lowest possible headloss. To improve the performance of duckbill check valves, valves have been recently developed in which the width of the bill is larger than the diameter of the cuff. The output area and the open position of the bill thus approaches more of the inlet area of the cuff, and the headloss decreases. For example, U.S. Pat. No. 5,931,197 to Raftis et al. discloses an asymmetrical check valve of this type.
It is therefore an object of the present invention to provide a duckbill check valve with an improved headloss over conventional valves. It is another object of the present invention to provide a check valve that overcomes the design problems encountered in the prior art.
The present invention is a check valve with an oversized bill. The present invention includes a tubular inlet part, an outlet part and a transitional middle part, connecting the inlet part with the outlet part, wherein the width or height of the outlet part is at least approximately 1.57 times the diameter of the inlet part. The outlet part may be symmetrical about a longitudinal plane through the check valve. It can also have a curved bill.
The advantage of a valve of this size is the low headloss compared to conventional duckbill check valves.
With an effective outlet area larger than the inlet area of the valve, the headloss will drop below the headloss of an open pipe end at high flow rates.
The invention itself, both as to its construction and its method of operation, together with the additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings.